This invention relates to illuminators for projection display systems, and more particularly relates to an arc lamp illuminator particularly suitable for use in a single panel scrolling color projection display system.
A single panel scrolling color projection display system is characterized by a single light modulator panel such as a liquid crystal display (LCD) panel having a raster of individual picture elements or pixels, which panel is illuminated by horizontally elongated red, green and blue illumination bars or stripes. The stripes are continuously scrolled vertically across the panel while synchronously addressing the rows of pixels with display information corresponding to the color of the then incident stripe. See, for example, U.S. Pat. No. 5,410,370, xe2x80x9cSingle panel color projection video display improved scanningxe2x80x9d issued to P. Janssen on Mar. 25, 1994, and U.S. Pat. No. 5,416,514, xe2x80x9cSingle panel color projection video display having control circuitry for synchronizing the color illumination system with reading/writing of the light valvexe2x80x9d issued to P. Janssen et al. on May 16, 1995.
Illuminators, commonly used in three panel liquid crystal display (LCD) projectors, utilize high intensity arc lamps to provide the level of intensity needed for projection systems. Such illuminators utilize lenticular arrays to homogenize the light from the arc lamp on the light valve, hence also on the screen. U.S. Pat. No. 5,986,809, describes an illuminator in which the uniformity of illumination is improved by separating a source beam into a plurality of intermediate beams that converge at a converging position, condensing the intermediate beams, spatially separating each of the intermediate beams into an S polarized beam and a P polarized beam, and then superimposing the polarized beams.
Although such illuminators indeed achieve a uniform illumination, angular space is not utilized in the best possible way. For a scrolling color system, which has a low angular extent, this leads to a lower brightness than is theoretically possible.
An arc lamp illuminator for a projection system includes one or more polarization conversion systems to laterally spread the arc image, creating one or more primary and secondary arc images. For a single panel scrolling color projection system, the primary and secondary images are spaced to allow for interleaving, to form an elongated arc image approximating the geometry of the scrolling stripe.
In its broadest aspects, the arc lamp illuminator comprises:
an arc lamp comprising an envelope enclosing an elongated arc having an axis lying in a lateral plane;
at least one projection lens for projecting an image of the arc;
at least one polarization conversion system oriented to split the projected arc image into primary and secondary arc images along the arc axis in the lateral plane; and
a rotator device for converting the polarization sense of either the primary or secondary arc image to correspond to the polarization sense of the other arc image.
In one embodiment, the arc lamp illuminator has a pair of projection lenses for projecting the arc image along first and second paths. For each path, the illuminator includes a polarization conversion system, a field lens for directing the projected arc image into the polarization conversion system, and a plane mirror for directing the projected arc image to the field lens.
The projection lenses may project the arc images along paths either in the lateral plane, in which case the plane mirrors are normal to the lateral plane to reflect the projected images to the field lenses.
Alternatively, the projection lenses project the arc images along paths above and below the lateral plane, and the plane mirrors are parallel to and lie above and below the lateral plane, respectively, to reflect the projected images to the field lenses.
In another embodiment, the arc lamp illuminator has three projection lenses for projecting the arc image along three different paths, a central path and two outer paths. For each path, the illuminator includes a polarization conversion system and a small mirror for directing the projected arc image into the polarization conversion system. For the two outer paths, a large mirror is provided for directing the projected arc image to the small mirror.
The polarization conversion system is typically embodied as a polarization conversion prism, while the rotator device is typically a quarter wave plate.
Compared to the prior art, this illuminator enables the use of longer arc lamps, and provides uniformity of illumination while maximizing brightness for a system having a low angular extent, such as a single panel scrolling color system.
The invention also includes a projection system including a light modulator panel for modulating a light image in accordance with an electrical signal; a lens for projecting the modulated image onto a display screen; and the arc lamp illuminator for illuminating the light modulator panel.